“Let me be clear: east Aleppo this minute is not at the edge of the precipice,” Stephen O’Brien told the Security Council.

“It is well into its terrible descent into the pitiless and merciless abyss of a humanitarian catastrophe unlike any we have witnessed in Syria,” said the UN undersecretary-general for humanitarian affairs.

The council was meeting to discuss the crisis in Syria as France said it would push for a UN resolution imposing a ceasefire in Aleppo, which has been under fierce bombardment by Syrian and Russian warplanes for a week.

US Ambassador Samantha Power described the escalation as “the most savage week we’ve seen in an incredibly savage five-plus-year war,” with more than 1,000 people killed by 1,700 air strikes on east Aleppo alone.

Power described the latest offensive as “soul-shattering” and accused Russia and Syrian President Bashar al-Assad of “unleashing a savagery” against civilians.

“We’re at a turning point,” she said.

O’Brien appealed for action from the council after diplomatic efforts on the sidelines of last week’s General Assembly meeting ended in failure, triggering a new upsurge in violence on the ground.

“This revolting situation in Aleppo must, please, be the SOS, the May Day call, to the international community,” he said.

“Syria is bleeding. Its citizens are dying. We all hear their cry for help.”

More than 100,000 children remain trapped in rebel-held east Aleppo, which has come under intense bombing since the Syrian army announced on September 22 an offensive to retake the city.

Aleppo, Syria’s second city, is divided between the rebel-held east and the government-controlled western part of the city.

The top UN aid official warned that evidence was being collected of the atrocities happening in Aleppo so that “one day there will be no hiding place” for those perpetrating war crimes.

French Ambassador Francois Delattre told reporters that France would “spare no effort” to try to impose a ceasefire in Aleppo through a UN resolution.

Russia however would likely use its veto power at the council to block such a resolution.